| What is hypothyroidism? | Common endocrine disorder, deficiency in thyroid hormone, defect in hypothalamic-pituitary-thyroid axis, vast majority caused by thyroid disease (primary hypothyroid) and less often secondary (decreased TSH) or tertiary (decreased TRH) |
| How is epidemiology of hypothyroidism? | Overt (0.1-1% in iodine depleted communities), subclinical (2-10% in adults w/increased prevalence w/age)
8-10 times more in women than men |
| What are clinical findings of hypothyroidism? | Variable depending on (age of onset, duration and severity of deficiency)
fatigue, cold intolerance, weight gain, constipation, myalgia and menstrual irregularities are prevalent among people w/normal thyroid function.
S&S if gradual are less prominent and more tolerated than if acute (thyroidectomy)
We have two changes induced by lack of thyroid hormone (slowing of metabolizing process causes fatigue slow movement weight gain, constipation, bradycardia, delayed relaxation of deep tendon reflexes. And accumulation of matrix GAGs leads to coarse hair and skin, puffy face, enlarged tongue, hoarseness: more in young pt) |
| List symptoms of hypothyroidism. | Fatigue, loss of energy, weight gain, anorexia, cold intolerance, dry skin, hair loss, sleepiness, muscle and joint pain, depression, forgetfullness, constipation, menstrual disturbance, decreased prespiration, blurred vision, decreased hearing, hoarseness
Physical signs (hypothermia, weight gain, slowed speech and movement, dry skin, jaundice, pallor, loss of scalp axillary and pubic hair, macroglossia, goiter, periorbital puffiness, decreased sys BP and increased dia BP, pericardial effusion, non pitting edema (myxedema), hypoflexia. |
| What are the major causes of hypothyroidism? | Primary (chronic autoimmune thyroiditis, iatrogenic (thyroidectomy or radioiodine), iodine deficiency or excess, infiltrative diseases (hemochroma, sarcoidosis), congenital thyroid agenesis/dysgenesis, drugs (lithium/amiodarone/IFNa/IL2), transient hypothyroid))
Central hypothyroid (TSH def, TRH def)
Generalized thyroid hormone resistane |
| What is chronic autoimmune thyroiditis? | Hashimoto's, most common cause of hypothyroid in iodine sufficient areas, cell-antibody destruction of thyroid, two forms goitorus and atrophic (differ in lymphocytic infiltration/fibrosis/follicular cell hyperplasia but not pathophysio)
High anti-TPO Ab or thyroid Na/I transporter in 90% of pt
Usually permenant (not always), and pt have family history of other autoimmune diseases |
| What is iatrogenic hypothyroid? | Thyroidectomy (occurs 2-4 weeks after thyroidectomy due to 7 day half life of thyroxine)
Radioiodine (I-131 for grave's can cause it months or years after admin)
External neck irradiation (doses 25 Gy or more, effect is dose dependent, gradual onset, most people are subclinical for several years) |
| What is iodine related hypothyroidism? | Both deficiency or excess could cause it.
Iodine deficiency (most common cause of hypothyroid and goiter worldwide, iodince intake <100micg/day, 2 billion people)
Iodine Excess (inhibits iodide organification and T4 T3 synthesis (Wolff-Chaikoff Effect), normal people escape this condition, but people w/abnormal thyroid don't and become hypothyroid w/in days |
| What drugs cause hypothyroidism? | Ones given to decrease thyroid secretion (methimazole, propylthiouracil (Perchlorate))
Ones used to treat non-thyroid conditions (lithium carbonate, amiodarone, IFN alpha, sunitinib) |
| What infiltrative diseases cause hypothyroid? | Fibrous thyroiditis (Reidel's thyroiditis), hemochromatosis, scleroderma, leukemia, cystinosis, sarcoidosis. |
| How is hypothyroidism in infants and children? | Most common cause is congenital (agenesis or dysgenesis of thyroid, inherited defect in hormone biosynthesis, mother taking antithyroid drugs for hyperthyroid)
Children w/ later hypothyroid the most common cause is chronic autoimmune thyroiditis. |
| What is transient hypothyroid? | Occurs in several types of thyroiditis, last from weeks to six months, pt with minimal symptoms may not require therapy, symptomatic ones should recieve T4 for several months and then stopped when we see recovery (normal TSH six weeks later) |
| What is secondary hypothyroidism? | Caused by TSH deficiency, 1% of hypothyroid, causes may be hypopituitarism or others (pituitary tumor, postpartum necrosis (Sheehan), hypophysitis, non-pituitary tumor (craniopharyngioma), infiltrative diseases, inactivation mutation of TSH or TSH receptor)
may be isolated TSH deficiency, but more often related w/other hormone deficiency. |
| What is tertiary hypothyroidism? | Caused by a damage in hypothalamus or hypothalamus-pituitary portal blood flow preventing TRH to reach pituitary.
Can be caused by mutation of TRH receptor.
Can be isolated or w/other hormonal deficiency, results from tumors, trauma, radiation, infiltrative diseases. |
| What is generalized resistance to thyroid hormone? GRTH | Rare disorder, auto dominant inheritance, mutation in gene of beta T3 nuclear receptor, so they have decreased affinity for T3 or can inhibit action of normal receptors.
Characteristic findings (high T3 T4, normal or high TSH) |
| How is dx of hypothyroidism? | Labs
Primary hypo (high TSH, low fT4). Subclinical hypo (high THS, normal fT4). Central hypo (low T4, TSH inappropriatly high) |
| How is the evaluation of hypothyroid? | Directed toward confirming dx and identifying cause of hormone deficiency (hx of meds/radiation, PE of goiter/thyroidectomy scar)
Pt w/ overt primary hypothyroid almost all have chronic autoimmune thyroiditis so we don't always need to get serum autoantibodies antithyroid.
Anti-TPO may be useful however to see progression from subclinical to overt |
| How is screening for hypothyroidism? | All pt w/ symptoms should be screened, pt seeking pregnancy, newly pregnant, undergoing evaluation asymptomatic pt should also be screenend for it by serum TSH levels
Thyroid function should also be seen for pt w/substantial hyperlipidemia, hyponatremia, high serum muscle enzymes, macrocytic anemia, pericardial/pleural effusion, previous thyroid injury, pituitary/hypothalamic disorders, hx of autoimmune diseases. |
| What is subclinical hypothyroidism? | Elevated TSH w/normal fT4, most often caused by autimmune (hashimoto) thyroiditis, anti-TPO pt w/ subclinical are at high risk to get overt.
May be associated w/increased risk of HF, CAD, coginitive impairment, non-specific symptoms of fatigue, mood alteration (middle aged pt).
Tx (can be observed w/out tx, or tx indicated if TSH>10 or TSH between 5-10 w/goiter or + anti-TPO, young pt |
| What are metabolic changes occurring during pregnancy leading to hypothyroidism? | Increased iodine renal clearance, increased TBG serum, inner ring deiodination of T3 and T4 by placenta, Stimulation by hCG, this causes a downwards shift in the normal range of TSH.
TSH assessment based on population trimesters (first: lower range decreased by 0.4 and upper by 0.5, then we have gradual return towards non-pregnant range in second and third trimesters) |
| What are maternal and fetal impacts on hypothyroidism? | - outcomes include miscarraige, prior to term delivery, fetal death, gestational HTN/preeclampsia, intrauterine growth restriction, low birth weight, decreased IQ |
| What are risk factors for thyroid dysfunction in pregnancy? | hx of thyroid disorder/symptoms, known thyroid Ab+ or goiter presence, hx of neck radiation or surgery, age >30, type 1 autoimmune diseases, hx of pregnancy loss/preterm delivery/infertility, multiple prior pregnancies (>3) family hx, morbid obesity, use of drugs, residing area w/low iodine |
| How is algorithm of hypothyroid tx | . |
| How should hypothyroid in women be treated? | • Aim for a TSH between lower reference limit and
2.5mU/L
• Increase their dose of LT4 by 20-30% as soon as
pregnancy is suspected or confirmed
• TSH should be monitored every 4 weeks untill mid gestation, and at 30 weeks |
